The present invention relates to a CMOS image sensor having one unit cell composed of two pixels, which is suited to a solid image pick up device such as a digital cameral or a camera system for mobile equipment.
As well known, a CMOS image sensor can be manufactured by the CMOS technology, which is widely used for manufacturing semiconductor devices having a small size and low power consumption and which can install a peripheral circuit such as a signal processor together with the image sensors in one chip. Thus, the CMOS image sensor is noticed as an alternative device to a CCD device conventionally used as an image pick up device.
A conventional CMOS image sensor is known, in which a unit cell Ce forming a pixel portion has two photodiodes PDa and PDb and one floating junction FJ, which is shared by the photodiodes PDa and PDb.
However, the conventional CMOS image sensor has pixels, which are arranged in a matrix having horizontal and vertical pitches of Ph and Pv respectively, which provide so long intervals between adjacent pixels in the horizontal and vertical directions that information between pixels cannot be picked up. Therefore, a problem arises that sufficient resolution of the sensor cannot be obtained. As a means for improving the resolution of the sensor, high integration of the sensor is conceivable. However, there is a limit in making the diodes and transistor elements constituting the pixel portion be reduced in their sizes and in making fine wires, thus there is also a limit in the improvement of the resolution of the sensor.
The present invention is made in view of the above-mentioned circumstances and it is therefore one of the objects of the present invention is to provide a CMOS image sensor, which make it possible to increase the integration by efficiently arranging elements and wires constituting the pixel portions without making the elements and wires small or fine and thereby to improve the resolution in the horizontal and vertical directions.